Politics Cymru understands that Bethan Jenkins and Leanne Wood are the 2 Plaid AMs who won't be voting with the Assembly Government on the controversial introduction of top-up fees in Wales.
They're backing a campaign by Cymru X (Plaid's youth wing) who are writing to the party's AMs asking them to maintain their policy.
Plaid have been accused of campaigning against top-up fees while voting with their Labour coalition partners to introduce them.
This issue also seems to be highlighting differences in approach within the party.
On last week's Politics Show Wales the Chair of Plaid Cymru, John Dixon, said that in government compromises have to be made while on Tuesday Plaid Minister Elin Jones defended the move and said that most of the party's AMs were supportive of the idea.
Ms Jenkins and Ms Wood therefore appear to be in the minority but could their rebellion be enough to cause damage to the coalition or to make their party's ministers think again?